The attack could be linked to sonic devices which emit inaudible soundwaves that can cause deafness, according to the Associated Press.

"We can confirm that at least 16 US government employees, members of our embassy community, have experienced some kind of symptoms," Ms Nauert said.

"We take the situation extremely seriously," she added.

Earlier this month two Cuban diplomats were expelled from Washington in response to the incident. Security around the diplomats’ residences in Havana has increased while America, Canada and Cuba search for answers.